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Cerfacs in brief

Centre of basic and applied research specialized in modelling and numerical simulation, Cerfacs, through its facilities and expertise in high-performance computing, deals with major scientific and technical research problems of public and industrial interest.

Cerfacs in motion

NEWS

OASIS3-MCT is a coupler of codes developed at Cerfacs and used around the world, mainly for climate modelling applications. Our last survey confirms that OASIS3-MCT is used by 67 modelling groups to assemble more than 80 different coupled applications over the 5 continents. These applications include global or regional configurations of ocean and atmosphere models but also sea ice, sea level, wave, ocean biogeochemistry, land, vegetation, river routing, hydrological and atmospheric chemistry models. OASIS3-MCT is used in 5 of the 7 European Earth System Models participating to the 6th Coupled Model Intercomparison Project (CMIP6) that produces the climate simulations forming the basis of the next report of the Intergovernmental Panel on Climate Change (IPCC)”Read more

The annual Sparse Days meeting will be held at CERFACS in Toulouse on 11th and 12th July 2019.
Registration for the Sparse Days is free but we ask people who are coming to register as soon as possible although the deadline is June 14th. Please complete the registration form (deadline : June 14th) indicating whether you want to give a talk and whether you wish to attend the conference dinner.
Although an emphasis will be on parallel aspects, any talk that has an association with sparsity is welcome.Read more

@ARTICLE{AR-CFD-19-120,
author = {Muscat, L. and Puigt, G. and Montagnac, M. and Brenner, P. },
title = {A coupled implicit-explicit time integration method for compressible unsteady flows},
year = {2019},
number = {Article 108883},
volume = {398},
doi = {10.1016/j.jcp.2019.108883},
journal = {Journal of Computational Physics},
abstract = {This paper addresses how two time integration schemes, the Heun's scheme for explicit time integration and the second-order Crank-Nicolson scheme for implicit time integration, can be coupled spatially. This coupling is the prerequisite to perform a coupled Large Eddy Simulation / Reynolds Averaged Navier-Stokes computation in an industrial context, using the implicit time procedure for the boundary layer (RANS) and the explicit time integration procedure in the LES region. The coupling procedure is designed in order to switch from explicit to implicit time integrations as fast as possible, while maintaining stability. After introducing the different schemes, the paper presents the initial coupling procedure adapted from a published reference and shows that it can amplify some numerical waves. An alternative procedure, studied in a coupled time/space framework, is shown to be stable and with spectral properties in agreement with the requirements of industrial applications. The coupling technique is validated with standard test cases, ranging from one-dimensional to three-dimensional flows.},
keywords = {Hybrid time integration, Space-time stability analysis, Finite volume formulation, Compressible unsteady flows},
url = {https://doi.org/10.1016/j.jcp.2019.108883}}

Le Bras, S., Deniau, H. and Bogey, C. (2019) A technique of flux reconstruction at the interfaces of non-conforming grids for aeroacoustic simulations, International Journal for Numerical Methods in Fluids, doi:10.1002/fld

@ARTICLE{AR-CFD-19-123,
author = {Le Bras, S. and Deniau, H. and Bogey, C. },
title = {A technique of flux reconstruction at the interfaces of non-conforming grids for aeroacoustic simulations},
year = {2019},
doi = {10.1002/fld},
journal = {International Journal for Numerical Methods in Fluids},
abstract = {A flux reconstruction technique is presented in order to perform aeroacoustic computations using implicit high-order spatial schemes on multiblock structured grids with non-conforming interfaces. The use of such grids, with mesh spacing discontinuities across the block interfaces, eases local mesh refinements, simplifies the mesh generation process, and thus facilitates the computation of turbulent flows. In this work, the spatial discretization consists of sixth-order finite-volume implicit schemes with low-dispersion and lowdissipation properties. The flux reconstruction is based on the combination of non-centered schemes with
local interpolations to define ghost cells and compute flux values at the grid interfaces. The flow variables in the ghost cells are calculated from the flow field in the grid cells using a meshless interpolation with radial basis functions. In this study, the flux reconstruction is applied to both plane and curved non-conforming interfaces. The performance of the method is first evaluated by performing two-dimensional simulations of the propagation of an acoustic pulse and of the convection of a vortex on Cartesian and wavy grids. No significant spurious noise is produced at the grid interfaces. The applicability of the flux reconstruction to a 3-D computation is then demonstrated by simulating a jet at a Mach number of 0.9 and a diameter-based Reynolds number of 4× 105 on a Cartesian grid. The non-conforming grid interface located downstream of the jet potential core does not appreciably affect the flow development and the jet sound field, while reducing the number of mesh points by a factor of approximately two.
}}